Successfully complete the game on the normal or hard difficulty setting.
Defeating Dorothy
When you start your first fight with Dorothy, attack with the Nalcon (green serum). Continue attacking her, and try not to stand on the lighted spaces and dodge the eyeballs. After crossing the bridge to fight Dorothy the second time, use your improved Nalcon to attack her. Note: She is much more powerful than she was the first time you fought her.
Defeating Nitro
When you go into battle with Nitro, you will find her very annoying. Use the following trick to damage her. When you first start, go near her and use the blue serum on her. It will make the things floating near her to go up. When the attack is charged, release and each floating thing will do over 700 damage to her. The serum can also be used as a shield from her attacks.
Defeating Parano
Parano is a very difficult Boss. Her weakness is Red or Fire. First, kill the four robots when you go in the room, then worry about Parano. You can only use Red to attack her. She gets mad after you hit her; get you shield ready. You need a lot of Recovery Pills if you are not very experienced. Keep attacking her with Red, then when she is hurt a lot she will start to spin and fly at you. Use your shield to block her. If you block her the first time, she will fly in circles around you. Start to charge your Red when she is doing this. As soon as she lands, you will be able to hit her if you are mentally locked on.
Defeating Spider
After defeating Dorothy in your first fight, you will go to the start of the level and make your way past the rooms. You will fight a boss named Spider. Try to move away from the dangling spiders. His weakness is Fire (red serum). When a spider gets on you press R1 (shield) to get them off. You cannot attack him with D-Felon (blue serum). When he comes down from his web, use Fire or Nalcon on him. After you defeat him, you obtain a Skip (allows you to improve a serum ability). Use your Skip on the Nalcon, as it will be needed later. Then, open the gate and cross the bridge to Dorothy.
Extra skip
In the Enriched Uranium Refinery, in the room where you format the security card to "Saturnus", defeat all the red and gray robots after you talk to Ash over the security screen.
Hard mode
Successfully complete the game on the normal difficulty setting with a "B" or higher rank to unlock hard mode.
Lv3PK mode
Successfully complete the game on the hard difficulty setting with an "S" rank to unlock Lv3PK mode.
Short mode
Successfully complete the game on the easy or normal difficulty setting to unlock short mode. Load the cleared saved game to toggle short mode.
Alternate ending sequence...